Radiant heating tubes are used to indirectly heat industrial furnaces. In such radiant heating tubes, the fuel utilization efficiency can be increased by preheating the air. So as to preheat the air, burners equipped with heat recuperators or regenerators are used. While, in general, the efficiency is greater in the case of burners equipped with heat regenerators, the apparatus-related complexity for the required switching mechanism is higher.
An industrial burner comprising a radiant tube and a recuperator or regenerators is known from DE 44 19 332 A1, wherein the heating of the radiant tube takes place by way of flameless oxidation. For this purpose, extensive recirculation of the flue gas is maintained in the radiant tube.
Due to preheating of the air, a drastic increase in thermal NOx formation in the flue gas can occur. The solutions proposed in DE 197 40 788 C1, DE 44 19 332 A1 or EP 2 184 538 A1 are primarily based on the method of combustion by flameless oxidation (FLOX®), including very strong recirculation of the combustion flue gases. However, the geometric shape of the radiant tubes must be suitable for this purpose. This is the case, for example, in what are known as P-tubes, double-P tubes or single-ended radiant tubes comprising flame tubes.
Due to installation space constraints in industrial furnaces, however, very thin radiant tubes having a ratio of the radiant tube diameter to the radiant tube length of less than 1:10 are required. The FLOX® combustion process having considerable recirculation for NOx reduction purposes is not a choice that can be considered here.